1. Field of the Invention
This invention relates generally to transmit/receive (T/R) devices used in apparatus such as radar equipment where an RF transmitter and an RF receiver are alternately coupled to and from an antenna and more particularly to a T/R module for planar active apertures of a phased antenna array.
2. Description of Related Art
Active apertures now being developed for radar, electronic counter measures (ECM), electronics security measures (ESM) and other types of microwave communications apparatus require structures that are thinner, lighter in weight, lower in cost and those that exhibit improved thermal expansion management along with requirement for easier maintenance. Planar phased arrays, which are generally known, lead to this end and involve structures where layers of RF manifold, DC power manifold, data distribution and cooling channels are assembled into a planar structure. In accordance with the known prior art, T/R modules including a patch type radiator on its outer surface are connected into the front of the array. One such T/R module is termed a "sugar cube T/R module" because it resembles a sugar cube in shape. However, the addition of increased functionality to such a T/R module such as a microprocessor based controller, increased memory, analog interface chips, digital interface chips, voltage regulator in other apparatus caused it to grow in length by approximately 4:1 and thus became rectangular in shape rather than square. Such a structure with patch type radiators cannot provide low radar cross-section or operating bandwidth required for a particular application and the heat which required dissipation had to be removed through a larger surface. The addition of functionality therefore caused the array design to change to a slat type configuration where, for example the T/R module function required its implementation in two separate packages on opposite side surfaces of a relatively long, thin plate radiator structure, thus giving rise to the name of a "slat" array.
It should be noted that T/R module architecture is closely related to the functionality required in the active aperture of the array in which it is used. Parameters that determine T/R module architecture are: (1) the need for low array sidelobes on receive; (2) the need for self-calibration in module to module built in test capability; (3) the need to maximize receiver input 3rd order intercept; (4) the need for low radar cross-section; (5) the need for low cost; (6) the need for maximized power added efficiency; (7) the need for radiating and receiving in various polarizations; and (8) the need for either distributed or centralized beam steering computation.